The secret with laptop batteries (in fact - any rechargeable battery in any appliance that offers mains or battery power) is to only use the battery when you are not near a convenient AC power outlet.
The worst thing you can do is to constantly run the laptop plugged into the mains with the battery fully charged. This will kill the battery in no time - a lot faster than repeated charge and discharge cycles, which will also lead to it's demise but at a far slower pace (all recharge batteries have a finite number of charge and discharge cycles before they WILL say cheers!).
So the rules are:
If away from AC power use the battery.
When back at your desk (or wherever) plug back into mains until the battery is fully recharged AND THEN DISCONNECT THE BATTERY FROM THE LAPTOP! Your laptop will now run on mains only and your battery will not suffer the damage caused by having a charge constantly rammed down it's throat.